1. Field of the Invention
This invention relates to a process for injecting air and water into a landfill to create anaerobic decomposition conditions and thereafter decreasing the volume of the landfill, i.e., the landfill air space by aerobic decomposition of decomposable municipal solid waste. Following municipal solid waste aerobic decomposition, the landfill may be mined in order to remove recoverable materials such as metals, plastics, glass and useful humus material. More specifically, this invention is a process and a landfill that includes a novel arrangement of wells for injecting moisture and air into a municipal solid waste undergoing aerobic decomposition in order to efficiently aerobically decompose waste.
2. Description of the Prior Art
The concept of aerobically decomposing a landfill to prepare it for a landfill mining is well known in the prior art. For example, in the article by R. I. Stessel et al. xe2x80x9cA Lysimeter Study of the Aerobic Landfill Conceptxe2x80x9d; Waste Management and Research 10:45-503 (1992) the authors describe a process whereby water and air are injected into municipal solid waste in order to aerobically decompose the waste. The article further discloses that following aerobic decomposition, the waste may be mined to remove recoverable materials. More specifically, the Stessel et al. article discloses the use of water including recycle leachate and air to aerobically decompose municipal solid waste at conditions including a moisture content of from about 50 to about 80%.
A similar article by R. J. Murphy et al. xe2x80x9cAerobic Degradation of Municipal Solid Wastexe2x80x9d For Presentation at 85th Annual Meeting and Exhibition, Kansas City, Mo. (Jun. 21-25, 1992) discloses aerobic decomposition studies performed on municipal solid waste at conditions including a temperature of from 30 to 89.4xc2x0 C. (85-192xc2x0 F.) an average moisture weight range of from 20 to 50% which was increased by leachate and water addition to a range of from 50 to 70%. The Murphy et al. paper also discloses that the aerobically treated municipal solid waste can be mined in order to recover the useful solid portions thereby allowing reuse of the mined landfill area.
Many issued U.S. patents also disclose process that employ aerobic decomposition processes. For example, U.S. Pat. No. 5,324,138 discloses an in-situ process for increasing the capacity of a municipal solid waste landfill using addition of moisture, lime, and physical disturbance to increase aerobic activity.
U.S. Pat. No. 5,356,452 discloses a process for recovering reusable materials subsequent to waste decomposition in an enclosed cell.
U.S. Pat. No. 5,265,979 discloses a high-efficiency waste placement and disposal method for solid waste in a landfill by reducing the size of the solid waste, adjusting the moisture, forming a waste pile, covering the waste pile, and compacting the waste pile. The disclosed method relies on slow anaerobic waste decomposition.
U.S. Pat. No. 5,702,499 discloses a batch process for the conversion of organic solid waste material through thermophilic aerobic digestion via mixing and moisture control.
U.S. Pat. No. 5,049,486 discloses a temperature monitoring method and apparatus for monitoring the temperature within a mass of organic matter moved through a composting vessel.
U.S. Pat. No. 4,077,847 discloses a system for segregating solid waste into ferrous metal, inorganic and organic fractions.
U.S. Pat. No. 4,410,142 discloses a method and an apparatus for composting waste using mixing and aeration.
U.S. Pat. No. 4,551,243 discloses a method to reduce the accumulation of undesirable solid material within an anaerobic digester.
U.S. Pat. No. 5,632,798 discloses a method for aerobic composition of organic waste material using high-flow aeration.
U.S. Pat. No. 5,584,904 discloses a process for reducing solid waste via shredding, anaerobic decomposition, aerobic decomposition, separation of the inorganic and organic waste, reduction of the plastic with solvents, and reduction of the metals with acids.
The prior art describes many methods and apparatus for decomposing municipal solid waste under aerobic or anaerobic conditions and/or mining aerobically or anaerobically decomposed landfills. There, however, remains a need for methods and landfill structures that enhance the delivery of water and air throughout a municipal solid waste a landfill in order to accelerate and control the aerobic decomposition of municipal solid waste.
The dwindling availability of space on which to site new municipal solid waste (MSW) landfills requires the consideration of reusing existing landfill space. Current bioreduction processes within MSW landfills are uncontrolled anaerobic processes that are inherently slow to occur and which produce high levels of methane gas along with malodorous trace gases. Controlled conversion of these anaerobic processes within MSW landfills to aerobic conditions is useful on a large scale basis as an alternative that will allow for a highly enhanced bioreduction of landfill mass over a much shorter period of time in comparison to conventional aerobic decomposition. The aerobic bioreduction of landfill mass may be followed by landfill mining of reclaimable/recyclable non-biodegraded materials, production of a high quality humus-like material, and reuse of a large volume, and possibly greater than 50 percent of the available landfill volume, thereby significantly extending the useful life of the MSW landfill.
This invention is a process for quickly and thoroughly aerobically decomposing municipal solid waste located in a landfill.
This invention is also a process that efficiently injects water and air into the interior of a municipal solid waste landfill in order to promote and control the aerobic decomposition thereof.
This invention is also a method for reducing landfill air space that uses a novel moisture and air injection system that safely controls the aerobic decomposition temperatures.
Furthermore, this invention is a landfill including a plurality of water and air injection wells located at defined lateral locations and depths with respect to one another in order to facilitate the efficient and controllable aerobic decomposition of landfill municipal solid waste.
In one embodiment, this invention is a method for reducing landfill airspace. The method includes injecting air and moisture into a landfill municipal solid waste layer that includes metal, plastic and biodegradable waste to produce aerobic conditions in at least a portion of the landfill. The moisture and air is injected into the landfill for a period of time sufficient to reduce the landfill airspace. The process improvement is characterized in that the air and moisture are injected into the landfill using a plurality of wells wherein at least one well comprises a bore hole containing a first air injection well located at a first depth below the landfill surface, and a second air injection well located at a second depth from the landfill surface where the first depth and the second depth is separated by a distance of from 10 to about 40 feet.
In another embodiment, this invention is a method for reducing landfill airspace. The method begins by injecting air and moisture into a municipal solid waste layer of a landfill wherein the municipal solid waste includes metal, plastic and biodegradable waste to produce aerobic conditions in at least a portion of the landfill. Air and water injection into the landfill are maintained for a period of time sufficient to aerobically decompose at least a portion of the aerobically decomposable landfill material to thereby reduce the landfill airspace. Following aerobic decomposition of the municipal solid waste, injection is halted and the landfill in mined to remove recoverable materials from the landfill. The process is an improvement over prior art processes in that the air and moisture are simultaneously injected into the landfill using a plurality of wells wherein each wells is separated from each other well by a lateral distance of from about 20 feet to about 100 feet, wherein each well includes a bore hole containing at least a first water/air injection well located at a first depth below the landfill surface, and wherein at least one well includes a borehole having first air and/or moisture injection point located at a first distance from the landfill surface, and a second air/moisture injection point located at a second depth from the landfill surface where the first depth and the second depth is separated by a distance of from 10 to about 40 feet.
In yet another embodiment, this invention is lined or unlined landfill including a plurality of air injection wells and a plurality of water injection wells wherein at least one injection well comprises a bore hole located in the municipal solid waste layer and containing a first air injection well located at a first depth below the landfill surface, and a second air injection well located at a second depth from the landfill surface where the first depth and the second depth is separated by a distance of from 10 to about 40 feet. The lined landfill embodiment of this invention will include one or more of the following elements: a clay seal layer, a liner, a permeable layer. The landfill will include a municipal solid waste layer having a depth of at least 20 feet wherein the liner, if one is used, is located between the clay seal layer and the permeable layer and wherein the permeable layer is located between the municipal solid waste layer and the liner. The unlined landfill embodiment of this invention will include municipal solid waste (MSW) in direct contact with natural materials or soils and mechanical and/or hydraulic barriers such as vertical or horizontal leachate wells.